Circuit arrangement embodying cathode-ray tubes



Apnl 12, 1949. E. w. BULL Erm. 2,467,009

' CIRCUIT ARRANGEMENT EMBODYING v CATHODE-RAY TUBES Filed Dec. 12, 194657540)' CUIVRE/V7 50i/ME Patented Apr. 12, 1949 UNITED STATES PATENTFFICE CIRCUIT ARRANGEMENT EMBODYING CATHODE-RAY TUBES ApplicationDecember 12, 1946, Serial No. 715,670 In Great Britain July 28, 1945Section 1, Public Law 690, August 8, 1946 Patent expires July 28, 1965 3Claims.

This invention relates to circuit arrangements embodying cathode raytubes in which the electron beam of the tube is required to be deflectedover a surface Within the tube.

In cathode ray tubes employed for television reception the fluorescentscreen of the tube is usually provided on the end wall of the tube, saidend wall usually being made as flat as possible in order to avoiddistortion of the optical image reproduced in the screen. Also incathoderay tubes employed for television transmission purposes themosaic screen of the tube is usually at. In deiiecting the cathode raybeam over the surface of such screens it is usually the practice toemploy two mutually perpendicular scanning fields and whilst it ispossible to cause the scanning beam to trace out a truly rectangularpatch on the screen providing that the screen has a surface whichapproximates to that of a sphere the centre of which is the point aboutwhich deflection of the beam occurs, it is found that when the screen isnot curved in such a manner the scanned patch is no longer rectangularbut is distorted. In cases where the screen is flat or of less curvaturethan the aforesaid sphere the scanned patch has a pincushion shape andin cases where the screen has a curvature greater than that of saidsphere the scanned patch has a barrel shape. In order to correct fordistortion of the scanned patch it has been the practice to vary thewaveform of the current or voltage employed for deffecting the beam orin the case of electromagnetic scanning so to dispose the conductors ofthe scanning coils that a eld is produced which diminishes in intensityfrom the axis of the tube. Although distortion of the scanned patch canbe reduced in this manner, it is found, however, that the variation infield intensity is such that considerable aberration or variation offocus of the cathode ray beam occurs at large angles of deection.

The main object of the present invention is to provide a circuitarrangement embodying a cathode ray tube in which improved means areprovided for reducing distortion of the scanned According to theinvention a circuit arrangement is provided embodying a cathode ray tubeand means for deecting the beam of said tube so that it can be caused toscan a patch .on the screen of said tube which patch would berectangular if the screen had a curvature corresponding to that of asphere having as its centre the point about which deflection of saidbeam occurs and wherein the screen has a curvature which is greater orless than that of said sphere and is arranged normally to the axis ofsaid beam and wherein there is provided means for setting up betweensaid screen and said point a eld which increases in intensity outwardlyfrom its axis so as to reduce substantially or eliminate eitherpincushion or barrel distortion which would occur in the absence of saideld.

Preferably said field is circularly symmetrical about the axis of thebeam in its undeflected position, and whilst such a eld is preferredapproximately circularly symmetrical elds can be employed.

The deflecting means employed may be either electrostatic orelectromagnetic or a combination of both electrostatic andelectromagnetic means and the means for setting up said field may alsobe electrostatic or electromagnetic.

In order that the said invention may be clearly understood and readilycarried into effect. the same will now be more fully described withreference to the accompanying drawings, in whichv Figure 1 illustratesdiagrammatically a circuit arrangement according to one embodiment ofthe invention employing electromagnetic means for setting up said eld,

Figure 2 is an end elevation on an enlarged scale of electromagneticmeans for setting up sai eld, and v Figure 3 illustrates electrostaticmeans for setting up said field. s

In Figure 1 of the drawings the reference nu, meral l indicates acathode ray tube having a substantially flat end wall 2 on which isprovided Aa fluorescent screen 3. The tube contains a cathode 4, acathode screen 5, a rst anode and a second anode l, these electrodesbeing fed in known manner with suitable potentials derived from a sourceof potential indicated conventionally by a battery across which isprovided a potentiometer 9 to which said electrodes are connected. Theelectron beam which is generated by the cathode 4 and focussed andaccelerated by the electrodes 5, 6 and 'l and which may be modulated byapplying suitable modulating pov 1 y f .tion of the beamcccurafthebeamwould trace out f f a truly :rectangular :patch on ,the screen.'y .The

. l present .invention .hou/even; concerned :with 1 cases 1in: whichfthe Ascreen d:i conforms to; al sur@ 1 face which. has a .curvature:which is i greater or; less: than; that ict said sphere sivhich of:course in-e =cludes thecase in which the screen eoniormstefaf f :dat fsurface Landf in; which the screen disposed 1 substantially normally tolth'e axisf or' fthe: beam whenundefiectem f In :suchA =cases: ifthe:bearnf isv i L deflected l over lthe surface f off the screen. :eitherzz :pincushion: or: :barrel distortions :occurs: :in the:

uscannedpatch.; -f l f l f :hilnonc fformfofl come :said: distortion fwhich; where f a dilat screen .is employed as in' Figure 12 the scannedpatch will 3 flrave; a pilnushidn shape; electromagnetic means y zareprovided. for setting` up a: @field between the scanning means and; thescreen gsad' meanszifor. s'etting' :up :said fe'ld beingy preferably:disposed 2 f lcloseitc! said@ scanning means. fPreferabiy; lthe E field.setz up is circularly symmetrical about the 1 faxis of; the' heaminzitsundeected position; Such afield is' :approximated by the arrangementshowin I 5in; Figure 2.. As: shownin this: tigure ithei means f iorsetting up said: field :comprises ai' circular ring ofr soft' iron l5lwhich `is 'preferably of laminated invention in' :order to':overconstruction and is provided with four coils i6 in series-aidingconnection Wound toroidally about symmetrically-disposed segments of thering 15. The ring I5 is arranged to surround the path of the beam asshown in Figure 1 and the axis of the ring is arranged coincident withthe axis of the beam in its undeflected position and the coils arearranged substantially opposite to the corners of the scanned patch. Thecoils IE5 may be fed with a steady current from a source l1 and thecoils are so arranged that they set up Within the ring l5 a eld whichincreases in intensity outwardly from its axis. In one specific exampleof the invention the end Wall 2 of the cathode ray tube I has a diameterof 12" and said end wall is substantially flat. The ring has an internaldiameter of 21/2" and an external diameter of 3 and is 1/2 thick. Eachcoil is Wound over 45 of the ring with 35 turns and may be fed with asteady current of 0.6 ampere. It is found that by employing such a eldthe electron beam can be caused to trace out a substantially rectangularpatch on the screen of the tube and that aberration of the cathode raybeam is reduced and that the focus of the beam can thereby be maintainedsubstantially constant throughout the scanning movement of the beam. Thedesired amount of correction imparted by the ileld can be adjusted byvarying the steady current passing through said coils.

The angle over Which each toroidal coil is Wound can be varied accordingto the correction required in individual cases, and, in general, where ahigh order of accuracy is required adtentials tothe electrode 'isindicated by the dote: I 'f f t v l ted .line Afl .and is caused totrace-r out 'a- :patch on L f i l :thefluore'scent screen. 3y fby-ydeiiecting the beam in two cio-ordinate :directions-.z =As shown linfFig.-v f

. ure i, the means :for deilectingzthe beam :com.

f .f prises two' .sets of :cuits :i E f and: L2 which are lfed f i l,with suitable currents: which, if Itl'le'tube lf :is c I ployedl for:television reception,A :are: generated by .f line and; frameirequencysawtoeth :generators it f and ll.A The :deflectingz means'employed for. .dee-c iiecting thebeam i l2= are :such that if :the:screen. f

: 1 i f 3 were disposed .on the .surface oi ta' sphere: hav. 2

i l ing as its centrethe :point about which fdenecaf .other than thatshown in Figure :Zimay :be ern-3 f c f fici s :arranged around: the;circumference :ci the :tub s .and :conform :to #the shape: of :a:circulary ring. and f extend overl segments. :of i thev circumference for f said ringsomewhat less: than: 45?'. Saidclectrodes. are disposed:substantially opposite to the corner f of: the: scanned patchandtocorrect for-pincnsho l distortion-said electrodes fwiil fbe fedwith; a sul f able fvzcltage; which isin'egative :with respect. tothwardly firom: its :axis

=' :In cases Where it: is desired to correct forA bar-= :rel fdistortion.the larrangement des.cribedz above s may; be employed but in such:'ca-'ses the direction f fot current fiowthrough the fc'oilsl llizWillbe iny the 1 opposite .direction to; that required A'for correcting1 f lpincushion distortion.` f Further; pincushion 1 .tcrtionz can be:corrected -byf changing Lthe position f :of the coilsfrcativeiyto thecorners: offthefscanned f insti-nent :of f the :currentkr in eachindividuati I coi 2 i :patch .and f employing the same: direction of fcurc f f renti'lour' as in the Acase for' correcting barrel fdistortion.and; vice versa.; :An arrangement iof .coi

z c flnstead ci' employing :electromagnetic means r f f r zfor settingup =saidsneld,= electrostatic: means f ma befempioyed shcwninigure saideilectrof-z f f static lmeans mayi comprise: =four electrodes i8`:Whichf may bel :disposed ion fthef Wali lof the tube: al :and suitably:spaced: or separated from the sec nd; anode the: electrode 4B beingequi-distanti.

otentialz appliied; to the :second: anode .t ;so` as; t

"' creases ini intensity fO.

c: with the: fbeam its= undeflected position The: fieldset: npzapproximates to .a:circulariy; symmetrical neldthat ris` to; -f

. say :azne'ld thelines of: which arel .crnica fconcle lInstead of:applyingasteady :current or `voitage f to the coils I6 or theelectrodes I8, a varying current or Voltage may be employed depending onthe form of the correction desired. For example, by feeding the coil l5or the electrodes I8 with a current or voltage of saWtooth Waveform, thefield in the region through which the beam is passing at any particularperiod during the deflecting cycle can be adjusted so as to give aneffect equivalent to a constant field of any desired law. The varyingcurrent or voltage can of course be employed in conjunction with asteady current or voltage.

Although the invention has been described above as applied to a cathoderay tube employing a uorescent screen, it will be understood that theinvention is not limited thereto since it can be applied to other typesof cathode ray tubes, such as those employing mosaic screens used intelevision transmitting tubes, such screens being usually supported inthe tube independently of the end wall of the tube.

What We claim is:

1. In cathode ray apparatus wherein there is provided a cathode ray tubehaving means for developing, deflecting, and directing a cathode raybeam toward a target area and in which the radius of curvature of thetarget differs from the distance from the point of deiection of the beamto the target, a plurality of beam inuencing means positioned adjacentsaid deflecting means and spaced apart equidistantly a pre-determinednumber of electrical degrees, and means for encrgizing said beaminiluencing means to produce a circularly symmetrical field about theaxis of the beam in its undeected position and which in- 5 6 creases inintensity outwardly from the axis of REFERENCES CITED the beam.

The following references are of record in the 2. Apparatus in accordancewith claim 1 wherein said plurality of beam influencing means le 0f thisPatenti Comprising a plurality Of windings each spaced P apart from theother by 45 electrical degrees and all energizing a core member oftoroidal shape. Number Name Date 3. Apparatus in accordance with claim 12,157,182 Maloi May 9, 1939 wherein said beam influencing means comprise2,164,931 Maloff July 4, 1939 electrostatic plates spaced apartl 45 fromeach 2,165,803 Maloi July 11, 1939 other. l0 2,230,111 GuntherJan.2s,1941 ERIC WILLIAM BULL 2,258,643 De Gier et al. Oct. 14, 19412,264,567 Gunther Dec. 2, 1941 MAX ERIC PEMBERTON.

2,406,740 Buckbee sept. 3, 1946

